1. Field of the Invention
The present invention relates to a video display apparatus, and particularly, to a signal transmission method and apparatus between appliances which are digitally connected.
2. Description of the Background Art
These days, A/V (Audio/Video) appliances operate digitally, and the digital A/V appliances are connected to each other by a digital network.
For example, a setup box and a digital TV are connected by an IEEE 1394 digital method, digital A/V contents (programs) are transmitted using an Isochronous Channel defined in IEEE 1394, and command language for control is transmitted in a AV/C (Audio/Video Control) format using Asynchronous Transaction.
In addition, an on-screen display (hereinafter, referred to as OSD) bitmap is transmitted through the Asynchronous Transaction using a method defined in an Asynchronous Connection protocol.
However, the bitmap image, such as an OSD transmitted between the A/V appliances, is used to notify a status or operation condition of the appliance, and transmission speed is an important element. However, if the image is transmitted through the digital connection, the transmission speed is lowered.
That is, the Asynchronous Connection used in the IEEE 1394 standard is a protocol originally used for transferring which should not include transfer error such as file transfer, and therefore, if the bitmap image such as OSD is transferred through the digital connection, the status and operation condition of the appliances can not be displayed in real-time.
Also, if the bitmap image, such as the OSD, is transmitted through the digital connection in the digital A/V appliances connected by the digital network, the resolution is lowered, and the status and operation conditions of the appliances are not easily recognized.